This invention relates to certain polymeric products prepared from pyridinium ylides. More particularly, it relates to hydrophophic, protective polymers and to articles, including photoresists, prepared from polymeric pyridinium ylides by a photolytic reaction.
The use of photopolymerization reactions in the printing and graphic arts fields for the production of relief and lithographic printing plates has been well known. Suitable methods for the production of plates for the printing and graphic industries are described, for example, in Neblette's Handbook of Photography And Repography, Seventh Edition, pp. 439-40 (1977). Typically, a monomeric compound on a suitable plate support material will be selectively exposed to a source of light so as to effect a photopolymerization (insolubilization) in exposed areas. The difference in solubility, between unexposed and exposed (polymerized) areas, permits easy development.
The principles of photopolymerization are also utilized in photoengraving and lithographic plate-making by the use of long-chain polymers whose molecules are able to crosslink under the action of light to form a three-dimensional molecular network. Typically, the photo-crosslinked polymer will be insoluble, and will be soluble only in powerful solvent mixtures of the type used in paint stripping. Stencils produced by the photo-crosslinking reaction are photoresists which are highly resistant to commonly used solutions; solvent development is used to remove the original long-chain polymer from unexposed areas.
In U.S. Pat. No. 3,081,168 (issued Mar. 12, 1963 to R. M. Leekly et al.), the production of relief plates using polyamides as a preformed polymer is described. Photosensitivity is imparted to the polyamide, which is carried on a support, by including with the polyamide, a photopolymerizable unsaturated compound. Following a selective exposure to light, which induces a decrease in solubility in exposed areas, unexposed areas are removed with a developer. After development, the base material (e.g., metal) can be etched by chemical etching or abrasive blast to form a relief image in the base material. If desired, an offset plate can be prepared by coating the photosensitive polyamide composition onto a hydrophilic support. The image obtained upon photoexposure and development will carry an ink and the wet support will resist ink.
In the production of plates by resort to photoreaction chemistry, a reactive and photopolymerizable monomeric compound will oftentimes be employed. The compounds are frequently liquid or in a gaseous form which may hamper efficient handling and the production of coatings suited to photopolymerization. Preformed polymers which are photo-crosslinkable may exhibit limited photo-reactivity or sensitivity. Accordingly, it will be appreciated that there will be application in photosensitive plate-making for a polymeric compound which can be conveniently coated from an aqueous medium onto a suitable substrate or carrier material and which can be readily converted, by a chemical modification induced by exposure to irradiation, to an insoluble or hydrophobic material.